1. Field of the Invention
The present invention relates to a process of producing a master carrier for magnetic transfer having a projection pattern for bringing it into intimate contact with a slave medium to magnetically transfer a desired magnetic pattern onto the slave medium, especially a master carrier for magnetic transfer in which a deficiency is hardly generated in a magnetic layer thereof.
2. Description of the Related Art
In magnetic recording media, media capable of undergoing so-called high-speed access, which have a mass storage volume so as to record a large quantity of information following an increase of the information amount, are inexpensive, and preferably, are able to read out a necessary portion within a short period of time, are desired. As one example thereof, high-density magnetic disk media to be used in hard disk units or flexible disks (hereinafter referred to as “FD”) are known. For the sake of realizing the mass storage volume, a so-called tracking servo technology in which a magnetic head accurately scans a narrow track width and reproduces a signal at a high S/N ratio bears a large role.
During one round of the disk, a servo signal for tracking, an address information signal, a reproduction clock signal, and the like are recorded at certain spacings as a so-called preformat. The magnetic head is set up in such a manner that it reads out such a signal of preformat and corrects its own position, whereby it can accurately run on the track.
At present, the foregoing preformat is prepared by writing the signals in every disk and in every track using a dedicated servo recording unit. The servo recording unit is provided with a magnetic head having, for example, a head width of about 75% of the track pitch. First, a disk is rotated in the state that the magnetic head is made closed to the disk, and signals of each track are written while moving the magnetic head every a half track pitch.
Since the foregoing servo recording unit is expensive and takes a lot of time for preparing a preformat, this step occupies the majority of the production costs. Thus, it is demanded to realize a low cost.
Then, a method of realizing this by magnetic transfer in place of writing of a preformat in every track is proposed (for example, see U.S. Pat. No. 6,347,016).
In this magnetic transfer, a master carrier having a projection pattern corresponding to information that is to be transferred onto a slave medium as a medium to be magnetically transferred, such as a magnetic disk medium, is prepared, and a transfer magnetic field is applied in the sate that the master carrier and the slave medium come into intimate contact with each other, thereby transferring a magnetic pattern corresponding to information (for example, servo signals) carried by the projection pattern of the master carrier onto the slave medium. According to this system, recording can be statically performed without changing the relative position between the master carrier and the slave medium, accurate preformat recording can be achieved, and the time required for recording is extremely short.
For the sake of enhancing the transfer quality in the foregoing magnetic transfer, how the master carrier is durable to the order of several thousands sheets in the good intimate contact state without causing breakage is important. That is, if the intimate contact fails, regions where the magnetic transfer does not take place are generated. If no magnetic transfer takes place, signal failure is generated in the magnetic information to be transferred onto the slave medium, leading to a lowering of the signal quality. In the case where the recorded signal is a servo signal, a sufficient tracking function is not obtained, resulting in a lowering of reliability.
FIG. 5 shows the production steps of a master carrier for magnetic transfer according to the related art.
According to this, a nickel (Ni) conductive layer is formed on a silicon support G1′ having formed thereon a pattern of a resist (R1) with projections, and a third ferromagnetic thick film F3 made of nickel as the major component is then formed by electroplating (see FIG. 5-(6)); and this is peeled from the resist pattern support G1′ to separate a resist R1 contact part of the third ferromagnetic thick film F3 side from a part (b) of the resist pattern support G1 (see FIG. 5-(7)).
After the separation, when the resist R1 of a part (a) of the third ferromagnetic thick film F3 side and dusts are cleaned up and removed by means of O2 ashing, etc., a nickel original plate F3 is obtained (see FIG. 5-(8)). A magnetic layer film F1 is laminated thereon by the sputtering method, whereby a master carrier M for magnetic transfer is obtained (see FIG. 5-(9)).
As the resist pattern support G1′, nickel, silicon, quartz plate, glass, aluminum, ceramics, synthetic resins, and the like are used. As magnetic materials of the magnetic layer film F1, Co, Co alloys (for example, CoNi, CoNiZr, and CoNbTaZr), Fe, Fe alloys (for example, FeCo, FeCoNi, FeNiMo, FeAlSi, FeAl, and FeTaN), Ni, and Ni alloys (for example, NiFe) are used.
As materials of the metal support F3, Ni or Ni alloys, etc. can be used. As the plating for preparing this support, a variety of metallic film formation methods including electroless plating, electroplating, sputtering, and ion plating were applied.
In the foregoing related art methods, the Ni conductive layer was provided on the resist support G1′ by film formation and subjected to electroplating to prepare the patterned Ni support F3; and the magnetic layer F1 was formed thereon by the sputtering method to form the master carrier M for magnetic transfer. When a number of sheets of slave media were subjected to magnetic transfer using the thus obtained master carrier M for magnetic transfer, transfer failure and breakage of the slave media occurred in the order of several thousands sheets.
Since it was thought that this is caused due to breakage of the master, the master was analyzed. As a result, it was ascertained that the magnetic layer formed on the patterned Ni support failed.
As a result of further investigations, it was noted from factorial separation experiments performed while taking the film thickness of the magnetic layer, etc. as a parameter that an internal stress in the magnetic layer was larger than the adhesive strength between the support and the magnetic layer, whereby peeling of the magnetic layer occurred therein.
It was noted that this phenomenon is liable to take place in the case of fine patterns of not more than 100 nm.
For the purpose of enhancing the adhesive strength, it was attempted to reduce the internal stress by changing the conditions of the Ni support surface treatment and the magnetic layer film formation. As a result, though a certain effect could be confirmed, a large enhancement was not achieved yet. In the light of the above, it was concluded that an improvement in the pattern coating property is necessary while ensuring an adhesive strength of a certain level or more between the magnetic layer and the Ni support.
In the foregoing related art methods, for example, if a soft magnetic layer made of FeCo is formed on the projection pattern formed by the Ni electroplating by the vacuum film forming method (for example, the spattering method), duration of FeCo piling (in the spattering process), it is rare that FeCo is piling on the projection while keeping the width of the projection, but FeCo is piling while also widening in the width direction. Therefore, in the projection pattern being finer than 100 nm, the piled FeCo films contact one another between adjacent projections, resulting in disordering of the pattern shape.